1. Field of the Invention
The present invention relates to a substrate pad structure that is configured to be connected to a lead terminal connecting portion of an electronic device that is mounted on the surface of a substrate.
2. Description of the Related Art
Conventionally, electrical connection between a substrate and an electronic device such as a connector that is surface-mounted on the substrate is established by attaching plural connecting portions of connector lead terminals to plural pads arranged on the substrate using solder, for example.
FIG. 1A is a diagram showing a coaxial cable connecter 150 being connected to one edge of an evaluation substrate 100 that evaluates transmission characteristics of a cable assembly. FIG. 1B is a diagram showing connecting portions 252 of lead terminals 250 of the connector 150 attached to pads 200 arranged on the substrate 100 so that electrical connection is established between the connector 150 and the substrate 100.
FIG. 2A is an enlarged view of the lead terminals 250 of the connector 150. The lead terminals 250 maybe positive signal terminals, negative signal terminals, or ground terminals that are connected to corresponding pads 200 arranged on the substrate 100. FIG. 2B is a diagram showing an arrangement of the pads 200 on the substrate 100.
FIG. 3A is a plan view of the connector lead terminals 250 connected to the pads 200. As is shown in this drawing, the connecting portions 252 of the connector lead terminals 250 and the pads 200 are arranged into oblong shapes with the pads 200 being slightly larger in size so that the connecting portions 252 of the connector lead terminals 250 may be soldered onto the pads 200. FIG. 3B is a side view of the connection between the connector lead terminal 250 and the pad 200. As is shown in this drawing, the entire bottom face of the lead terminal connecting portion 252 comes into contact with the surface of the pad 200.
It is noted that Japanese Laid-Open Patent Publication No. 5-63132 discloses a technique for accurately connecting lead terminals to pads of a substrate without having any positioning deviations by adjusting the shape of the lead terminal.
However, when the entire bottom face of the lead terminal connecting portion is arranged to come into contact with the surface of the pad, characteristic impedance matching may not be adequately performed when transmitting a signal of a high frequency range and signal reflection may occur so that transmission characteristics may be prone to degradation.